By merely turning the plus or convex spherical reel inward, or toward the patient’s nose, the convex power is then decreased, naturally increasing the concave value or total minus lens power. For example, if the spherical indicator shows +5.D, when the -6D. lens is placed behind it, the lens value at the sight opening will be -1D ([Fig. 6]). If required, the refractionist may continue on this plan until only the -6D. lens remains.
Fig. 6—With this indicator of supplementary disk, set at -6.D. Sph. and spherical indicator at +5.D—lens value at sight opening is -1.D. Sph. This simple arrangement makes it possible to operate the Ski-optometer with but Single Reel for both plus and minus sphericals.
Should concave power stronger than -6D. be desired, by placing the pointer of the supplementary disk at -12D. Sph. and proceeding to neutralize as before, all the concave powers up to -12D. in quarters are similarly obtained. For the convenience of the operator, all minus or concave spherical powers are indicated in red; while plus, or convex powers, are indicated in white.
The instrument is also provided with an opaque or blank disk which is brought into position before the sight opening by setting the pointer of the supplementary disk at “shut” ([Fig. 3c].)
Summing up, all plus and minus spherical powers have been attained from zero to 12D. in quarters, practically through the turn of the single reel—a simplicity of operation largely responsible for Ski-optometer supremacy.
Chapter II
CYLINDRICAL LENSES
It is commonly admitted that setting each trial-case cylindrical lens at a common axis is the most tedious part of refraction.
The automatic cylinder, one of the Ski-optometer’s latest and distinctly exclusive features, not only overcomes this annoyance but also avoids the need of individually transferring each cylindrical lens according to the varying strengths.
